text:
Are there diversion points for southern Pacific great circle route flights?
At first I wasn't even sure if any airlines flew southern Pacific great circle route flights, but it looks like Qantas (QFA27) operates a flight between Sydney and Santiago, Chile.
For northern Pacific greate circle routes, you are flying near Canada/Alaska and then Russia for most of the flight, so you have some airports you could potentially divert to if an emergency arose. I've search online for more details about how this works for these flight, but haven't had much luck finding information.
Are there any point on the southern Pacific great circle route for flights to divert to? Or is there not really any backup plan if something goes wrong? Are there specific requirements that must be met for an aircraft to fly this route?

If you only have 2 engines, you play by the ETOPS rules (Engines Turn Or People Swim) and there are specific rules about distances to alternates at any given point on your route.  If you have 4 engines, you have more leeway on alternates.  I don't have the specifics to give you an answer, but hopefully someone else can provide that.

@casey The new(er) ETOPS rules actually apply to all airplanes, not just two engine airplanes like in the past.

amazing QA here !

This particular flight was a Boeing 747 flying from YSSY (Sidney) to SCEL (Santiago).  Because a 747 has more than two engines, they don't have specific time limits on how far from land that they can fly like two engine airplanes do.
That being said, they do have to carry enough fuel to make it to a suitable airport in the event that the airplane depressurizes or it has an engine failure at any point along their route.1.  This doesn't mean that they have to make it all of the way to their destination in the event of a problem though.  They use en-route diversion airports and have predefined points on their flight plan which tell them where to divert to at any given point during the flight.
You will notice on this flight (see the images below) that their planned route is considerably further North than the shorter great circle route.  This is probably so that they can use NTAA (Tahiti) as a diversion airport if they have a problem.  The route is also optimized for the current winds at the cruising altitude, so it may be more fuel efficient to go out of the way in order to have more favorable winds.
In this case, without seeing their actual dispatch paperwork we can't know for sure whether or not they could have even flown the great circle route with the amount of fuel that the airplane can hold, but we'll just assume that they are using NTAA as an ETOPS airport for the purposes of this discussion.  That being said, we will use the following airports as our ETOPS diversion airports:  NZCH, NTAA, and SCEL.  In this case, their diversion plan in the event of an emergency would probably be something like this:

From takeoff (YSSY) until a point a little less than half way to NZCH (New Zealand)2 they would divert back to their point of departure2
From a little less than half way to NZCH until a point around 46W52 they would divert to NZCH.
Between the points that would be around 46W52 and 47W25 they would divert to NTAA.
After 47W25 they would continue on to their destination (SCEL) because it would be faster than turning around and going back to any of the other airports.

Each of the points takes wind into consideration, and as they pass each one they will always know which airport that they can reach in the least amount of time.  The most important thing is that they always have enough fuel to make it somewhere safe in the event of an emergency.

Filed Route

Great Circle Route

1 They also have to carry enough fuel to fly to their alternate airport and additional contingency fuel.  One thing to keep in mind is that a jet burns considerably more fuel at low altitudes than they do at their optimum altitude, so they have to carry a lot of extra fuel to meet this (and other) requirement.
2 If they turned around at the exact halfway point, it would take them longer to return than to continue because of the East winds.

Regulations
For those of you interested in the actual fuel requirements for a flight like this, the US regulations are listed in 14 CFR 121.  I'll use these as an example (other countries will be very similar, but I know these.)
You will notice that almost every line of the regulations listed here will require extra fuel to be on board the airplane. (Look for the ✈ symbol next to each one that I have added.)  Fortunately, it isn't quite as bad as it looks though, because some of the fuel that is pumped into the airplane can be used for more than one purpose.  For instance, a portion of the fuel may be used to divert to an ETOPS airport and used to fly to your destination, because they will only be doing one or the other.  The pertinent regulations are summarized here:

§121.645 - Fuel supply: Turbine-engine powered airplanes...
...
(b) For any certificate holder conducting flag or supplemental
  operations outside the 48 contiguous United States and the District of
  Columbia, unless authorized by the Administrator in the operations
  specifications, no person may release for flight or takeoff a
  turbine-engine powered airplane (other than a turbo-propeller powered
  airplane) unless, considering wind and other weather conditions
  expected, it has enough fuel—
✈ (1) To fly to and land at the airport to which it is released;
✈ (2) After that, to fly for a period of 10 percent of the total time
  required to fly from the airport of departure to, and land at, the
  airport to which it was released;
✈ (3) After that, to fly to and land at the most distant alternate
  airport specified in the flight release, if an alternate is required;
  and
✈ (4) After that, to fly for 30 minutes at holding speed at 1,500 feet
  above the alternate airport (or the destination airport if no
  alternate is required) under standard temperature conditions.
...
§121.646 - En-route fuel supply: flag and supplemental operations.
(a) No person may dispatch or release for flight a turbine-engine
  powered airplane with more than two engines for a flight more than 90
  minutes (with all engines operating at cruise power) from an Adequate
  Airport unless the following fuel supply requirements are met:
(1) The airplane has enough fuel to meet the requirements of
  §121.645(b);
✈ (2) The airplane has enough fuel to fly to the Adequate Airport—
✈ (i) Assuming a rapid decompression at the most critical point;
✈ (ii) Assuming a descent to a safe altitude in compliance with the
  oxygen supply requirements of §121.333; and
✈ (iii) Considering expected wind and other weather conditions.
✈ (3) The airplane has enough fuel to hold for 15 minutes at 1500 feet
  above field elevation and conduct a normal approach and landing.
(b) No person may dispatch or release for flight an ETOPS flight
  unless, considering wind and other weather conditions expected, it has
  the fuel otherwise required by this part and enough fuel to satisfy
  each of the following requirements:
✈ (1) Fuel to fly to an ETOPS Alternate Airport.
✈ (i) Fuel to account for rapid decompression and engine failure. The
  airplane must carry the greater of the following amounts of fuel:
✈ (A) Fuel sufficient to fly to an ETOPS Alternate Airport assuming a
  rapid decompression at the most critical point followed by descent to
  a safe altitude in compliance with the oxygen supply requirements of
  §121.333 of this chapter;
✈ (B) Fuel sufficient to fly to an ETOPS Alternate Airport (at the
  one-engine-inoperative cruise speed) assuming a rapid decompression
  and a simultaneous engine failure at the most critical point followed
  by descent to a safe altitude in compliance with the oxygen
  requirements of §121.333 of this chapter; or
✈ (C) Fuel sufficient to fly to an ETOPS Alternate Airport (at the one
  engine inoperative cruise speed) assuming an engine failure at the
  most critical point followed by descent to the one engine inoperative
  cruise altitude.
✈ (ii) Fuel to account for errors in wind forecasting. In calculating
  the amount of fuel required by paragraph (b)(1)(i) of this section,
  the certificate holder must increase the actual forecast wind speed by
  5% (resulting in an increase in headwind or a decrease in tailwind) to
  account for any potential errors in wind forecasting. If a certificate
  holder is not using the actual forecast wind based on a wind model
  accepted by the FAA, the airplane must carry additional fuel equal to
  5% of the fuel required for paragraph (b)(1)(i) of this section, as
  reserve fuel to allow for errors in wind data.
✈ (iii) Fuel to account for icing. In calculating the amount of fuel
  required by paragraph (b)(1)(i) of this section (after completing the
  wind calculation in paragraph (b)(1)(ii) of this section), the
  certificate holder must ensure that the airplane carries the greater
  of the following amounts of fuel in anticipation of possible icing
  during the diversion:
✈ (A) Fuel that would be burned as a result of airframe icing during 10
  percent of the time icing is forecast (including the fuel used by
  engine and wing anti-ice during this period).
✈ (B) Fuel that would be used for engine anti-ice, and if appropriate
  wing anti-ice, for the entire time during which icing is forecast.
✈ (iv) Fuel to account for engine deterioration. In calculating the
  amount of fuel required by paragraph (b)(1)(i) of this section (after
  completing the wind calculation in paragraph (b)(1)(ii) of this
  section), the airplane also carries fuel equal to 5% of the fuel
  specified above, to account for deterioration in cruise fuel burn
  performance unless the certificate holder has a program to monitor
  airplane in-service deterioration to cruise fuel burn performance.
✈ (2) Fuel to account for holding, approach, and landing. In addition to
  the fuel required by paragraph (b)(1) of this section, the airplane
  must carry fuel sufficient to hold at 1500 feet above field elevation
  for 15 minutes upon reaching an ETOPS Alternate Airport and then
  conduct an instrument approach and land.
✈ (3) Fuel to account for APU use. If an APU is a required power source,
  the certificate holder must account for its fuel consumption during
  the appropriate phases of flight.
§121.647 - Factors for computing fuel required.
Each person computing fuel required for the purposes of this subpart
  shall consider the following:
✈ (a) Wind and other weather conditions forecast.
✈ (b) Anticipated traffic delays.
✈ (c) One instrument approach and possible missed approach at
  destination.
✈ (d) Any other conditions that may delay landing of the aircraft.
For the purposes of this section, required fuel is in addition to
  unusable fuel.

As it happens I am living in the southern part of New Zealand (Te Anau) where there is virtually no airliner traffic overhead - except for QF27. On a clear day, they will usually be making contrails so quite evident. So sorry to digress from your detailed post but the flightpath is quite a bit more south than the image you have posted. I checked on flightradar24 and the track is in fact even more south than me (I'm about 45.5S) Plus they will likely be adhering to Australian CASA regs flying VH registered aircraft but the equivalent FARs are probably easier to find. But great post.

@timbo Great, thanks for the info!  As I mentioned, the winds play a large role in route selection, so this particular flight may not be the optimum flight all of the time.  Welcome to the site!

Quibble - from about halfway between 46W52 and 47W25 to about halfway between 47W25 and SCEL, SCIP would be a better option than either NTAA or SCEL, what with being (sometimes considerably) closer and all.

@Sean That might be a good diversion airport to use, but I noticed on their wiki that they severely restrict the number of airplanes that can use it (only one airplane at a time can be in the area that can divert to it).  I'd have to run the flight plan again to see if it even helped, but good find!

@Lnafziger: True, but, since that flight is passing through said area of airspace anyways, it doesn't matter whether it actually intends to land at SCIP or not - while it's within SCIP's sphere of influence, no other aircraft can be in that airspace, and vice versa (what if they had an emergency necessitating an immediate landing at the nearest airport, which happened to be SCIP, and the runway was blocked by another aircraft?).

On the great circle route from Sydney to Santiago, from southern New Zealand (past Invercargill, maybe) to southern Chile, there is a stretch of about 4,000 nm with no landing sites.
There are specific requirements for air carriers for "extended overwater operations." These take into account the aircraft range after engine failure, distance to diversion airports, emergency equipment and training, etc. There is definitely a backup plan in place for every overwater airline flight.
A twin engine jet airliner will have an ETOPS (Extended range Twin Operations) rating that is the distance it able to reliably fly, fully loaded, on one engine. Many Boeing 777s have an ETOPS rating of 330 minutes, for example, which means they must fly on a route that keeps them within 5.5 hours of an airport at single engine speed.
Airliners conducting extended overwater operations must be ditching certified, which involves aircraft design, emergency equipment, and crew training for emergency water landings.


text:
Why do commercial flights turn / bank so sharply?
When I take commercial flights, or you see turns in the vapour trails, they turn very sharply. What's the reason for this - wouldn't it be more efficient to turn gradually?

Are you asking why airplanes make "sharp" turns, or are you asking why they're making turns at all (going in a straight line from A to B is, after all, a lot more efficient)?

Lnafziger's answer below is correct in that a higher speeds it requires more bank to maintain a standard rate. That said, 30 degrees of bank is more typical of how pilots fly with passengers. 30 degrees of bank is nothing really to a pilot. Even at the most basic Private Pilot (US) standard in a small airplane the minimum required is to demonstrate 45 degrees of bank and up to 60 is allowed for the aircraft. Aerobatic airplanes can do 70-80 degrees of bank while maintaining level flight, they can even flip over 180 degrees and fly upside down.

FWIW, the last 747 carrier I worked for had a statement in their ops specs that banks should be limited to 20 degrees when within 4000 feet of the ground for passenger comfort unless there was an overriding need to bank steeper.

This landing from the South includes reversing course by 180° at about 5 km from the threshold with two 90° left turns. Does that match your observations?

Airplanes are expected by air traffic control to turn at a "standard rate of turn" which is 3 degrees per second.  This will provide a 90 degree turn in 30 seconds.  A standard rate is used so that controllers can anticipate how long it takes for an airplane to turn to a heading and they can line them up easier.  It also makes the turn happen in a smaller amount of airspace so that two airplanes can be flying in the same general vicinity without getting too close.
Unfortunately, at the speeds that jet airplanes travel this would mean a very high angle of bank.  A standard rate turn at 200 KT TAS is about 30 degrees of bank and jets can go much faster than this, which would require even higher bank angles.  They actually limit it to 25 degrees of bank when using a flight director, mainly for passenger comfort.
It can be impressive when looking out the window and seeing the ground, but don't worry, the airplane is more than designed for it!
This is used mainly at lower altitudes where there are lots of airplanes.  Once they are up high and airplanes are further apart (and the turns are also usually smaller) they  can bank even less (by using a "half-bank" mode) which adds to passenger comfort.

30 seconds for a quarter turn at a speed of 878km/h means a turning radius of 4.6km

I always thought large aircraft use half rate turns (4 minute turns instead of 2 minute ones), but I can't find authoritative reference and can't find definition of "large" for this purpose.

There is another question for explaining this.

@JanHudec The FAA definition of "large" is any aircraft weighing more than 12,500 lbs. (14 CFR 1.1).  As far as the other question, he asked it after seeing the answer to this one (and this answer kind of answers that too, by explaining how fast they actually turn. :) )

Airliners actually turn relatively slowly, but are often so far away (when viewed from the ground) that they appear to be turning sharply. An airliner cruising at 35,000 feet is actually over 7 miles away, which makes scale hard to comprehend.
From the air, riding in an airliner, you may be confusing rate of turn with roll rate or angle of bank. An airliner will roll relatively smoothly into a bank angle of up to 30° (which can seem steep), and a rate of turn (change in compass heading) of between 3° and 1.5° per second. You often don't feel the roll, but will observe the bank by looking out the window.
The reason for the 1.5-3° turn rate is so that Air Traffic Control can have some way to predict where an aircraft will be in x seconds. Rate of turn is standardized, making that possible.

"An airliner cruising at 35,000 feet is actually over 7 miles away, which makes scale hard to comprehend." And that's if it's almost directly overhead. If they appear to be near the horizon and they're flying at that altitude, they could be 100 mi or even 200 mi away on a clear day, especially if your horizon is clear of obstacles.

Most aircraft tend to make standard rate two-minute turns, as in it would take them two minutes to turn 360 degrees (3 degrees per second). At higher altitudes and higher speeds (or heavier aircraft) they might do half-rate (four minute) turns, which are 1.5 degrees per second.
So at a higher speed (which high-flying planes are likely to be at), to turn a the same rate, they must bank more sharply. That's why at higher speeds the halve the rate, so they can reduce the required bank angle.
More likely though, it's just your perspective. From your position on the ground it looks like they're turning sharply but in reality it took them several miles to make the turn. From your position in the plane, it's difficult to comprehend how fast you're going.
Finally, at higher airspeed speed sharper bank angles are required to keep the plane coordinated during a standard rate turn. This means that when you turn, you feel like you're being pressed down into your seat instead of sideways out of it (like when you take a turn fast in a car).

Hmm, your last paragraph reads like you are saying that an airplane can't be coordinated at a small angle of bank....?

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What happens when a helicopter loses an engine?
It seems like at this point it would be game over, since the spinning rotor is the only thing keeping it in the air. Is there any way to land a helicopter in this condition without crashing?

In some helicopters with high inertia rotor systems (basically heavy and store a lot of energy simply through rotation), auto rotations can be non-events.  The B47 could be landed, picked up, turned through 180 degrees and put down again all without the engine.  The other great thing about engine failures in many helicopters is that they need a lot less space than a fixed wing.  I know some really good pilots who need something about the size of a cricket pitch.

Helicopters are able to do something called autorotation if all thrust is lost.

In a helicopter, an autorotative descent is a power-off  maneuver in
  which the engine is disengaged from the main  rotor system and the
  rotor blades are driven solely by the  upward flow of air through the
  rotor. In other  words, the engine is no longer
  supplying power to the main  rotor.

(Look in particular at the direction of flight arrows. Remember there's a lift vector coming of the blades as well in both cases.)
Basically, the collective is decreased immediately when thrust is lost for whatever reason. This allows the airflow coming through the blades to push them around, like a reverse windmill in a way, keeping the blades spinning. This also generates lift, keeping the helicopter generating some lift (while descending of course).

At the instant of engine failure, the main rotor blades are
  producing lift and thrust from their angle of attack (AOA)
  and velocity. By lowering the collective pitch, which must be
  done immediately in case of an engine failure, lift and drag
  are reduced, and the helicopter begins an immediate descent,
  thus producing an upward flow of air through the rotor
  system. This upward flow of air through the rotor provides
  sufficient thrust to maintain rotor rpm throughout the descent.
  Since the tail rotor is driven by the main rotor transmission
  during autorotation, heading control is maintained with the
  antitorque pedals as in normal flight.

Once the helicopter reaches ground, the pilot will pull up. Since the blades were spinning a bit faster than needed for a hover since he was flying forward the whole procedure, he simply pulls up and levels out carefully close to the ground until the helicopter touches down.
This being said, you have to be careful, since if you're flying to slow you can't pull it off.

When landing from an autorotation, the only energy available
  to arrest the descent rate and ensure a soft landing is the
  kinetic energy stored in the rotor blades. Tip weights can
  greatly increase this stored energy. A greater amount of rotor
  energy is required to stop a helicopter with a high rate of
  descent than is required to stop a helicopter that is descending
  more slowly. Therefore, autorotative descents at very low or
  very high airspeeds are more critical than those performed
  at the minimum rate of descent airspeed.

This dangerous conditions are shown in a height-velocity diagram as is seen below, in this case apparently from an R44.

Here's a little video to get an idea of how it looks for the pilot:

Autorotation is often time critical and has to be done right as there's only one shot and as such is practised by pilots on a regular basis.
All extracts in this section are from "Helicopter Emergencies and Hazards" by the FAA, an excellent and very extensive publication on the topic.

Many helicopters have more than one engine driving the rotor system.  On those, losing an engine is probably less serious than it would be in a single-engine craft.
All helicopters that I'm aware of are capable of autorotation.  In an autorotation, the pilot uses the air rushing up through the rotor disk to keep the blades spinning. This involves changing the collective angle of attack of the blades to near zero to minimize drag, plus some other control inputs.
While doing this, the pilot is trading potential energy (altitude) for kinetic energy (keep the rotors spinning).
Immediately prior to landing, the pilot changes the collective angle of attack of the rotors back to the normal "push air down" setting. This rapidly slows the rotors, but if done correctly there's enough cushion to land the vehicle.
For a much more detailed description of how to execute an auto-rotation landing,
see How does a helicopter pilot execute an auto-rotation landing?
Per FAR 61.87(f)(15), A student pilot who is receiving training for a helicopter rating must receive and log flight training for the following maneuvers and procedures:
...
(15) Simulated emergency procedures, including autorotational descents with a power recovery and power recovery to a hover;

I'm pretty sure helicopter pilots are taught autorotation prior to solo, but can't confirm right now.

This article has a pretty good illustration of what you're talking about.  And the article also seems to confirm your comment. http://www.todayifoundout.com/index.php/2012/05/helicopters-wont-just-fall-like-a-rock-if-the-engine-dies-they-usually-can-be-landed-safely-this-way/

@DanPichelman they do, 61.87(f)(15) requires it.  I have 0.3 in an R22 and even I have had it demonstrated and practiced.

How did this get 17 upvotes?  Sorry, but it's just plain misleading.  2nd paragraph, wrong.  With the exception of a wider "allowed RPM" band, the rotor spins at the same speed as in normal flight.  3rd paragraph, misleading.  the pilot does not "tilt the rotors" back to a "normal" setting.  The pitch of each blade is increased collectively to increase the angle of attack and therefore the lift.  But this is only possible if you have already reduced the rate of descent significantly and flared to convert the remaining speed into rotor RPM.

@Simon - thanks for the corrections.  I've updated the answer so it's hopefully more accurate.  I will be happy to make further changes if I've still missed something.

Read my answer here then consider a few more edits.

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Where does the term 'steam cockpit' come from?
Why are traditional style cockpits with gauges called 'steam cockpits'? Do the instruments actually run on steam?

The term is actually "steam gauges" - I've never heard anybody refer to a "steam cockpit".

I think it's simply because glass dial gauges resemble steam pressure gauges (e.g. on a steam engine, turbine, whatever). Certainly no aviation instruments have ever run on steam that I'm aware of.

@dvnrrs well, there is steampunk, but they usually prefer airships ;-)

I don't know about the instruments, but the engine of at least one airplane ran on steam.

Well, some flight simulators probably run on Steam...

Well, to answer your second question first: no.  No aircraft instruments actually run on steam.  There are lots of safety issues related to generating and using the steam on board an aircraft that are prohibitive.
As far as why they are called steam gauges, take a look at one and compare it to a traditional flight instrument:

They are both round, both have a calibrated scale printed on  them, and both have a needle which points at the current value.  They actually look pretty similar!

so is a car speedometer/tachometer also a steam gauge?

Heh, I always thought "steam gauges" referred to vacuum gyro-instruments (as they work the same way, only backwards, pulling air out rather than pushing steam in..)

@shortstheory I've never heard them called that, but aviation is a more technical field so maybe it arose from people who worked wih both, back in the early days.

@falstro Well,the airspeed indicator, the altimeter, and the VSI are not vacuum powered but are called steam gauges!

@Lnafziger Oh I'm sure you're right! I just thought it was interesting how much we just assume sometimes :)

@Lnafziger: They're called "vacuum gyro-instruments" because the instruments measure the outputs of a vacuum-powered gyro. In other words, the vacuum makes the gyro spin. The instruments that measure the gyro (attitude, heading) are not themselves directly measuring pressure, as opposed to the airspeed indicator and altimeter, which are examples of instrments that directly measure pressure (just like a steam gauge).

I never heard the term "steam gauge" until there were glass cockpits - but maybe that is just me.  A "steam gauge airplane" is a mildly derogative term to indicate that the plane has instruments that are old fashioned, borderline obsolete.  But they work just fine!  I fly a steam gauge airplane.

Live and learn, I guess. This question was the first time I've ever heard the term "steam cockpit." This is all making me feel really old.

@Terry I've never heard the term "steam cockpit" either, but "steam gauges" are a relatively common term now.

Well, before glass cockpits all instruments were of the "steam gauge" type, so there was no need to have a name for them.

There would never have been a reason to call them "steam" gauges until the emergence of glass cockpits. As a term to distinguish between them, "steam" would certainly suggest an image of round gauges with moving mechanical pointers commonly seen on steam-powered equipment. "Glass" cockpit seems a funny term... "steam" gauges have glass faces on them, just like digital displays do.

Skip's experience in the emergence of the term matches mine, in terms of arising only when glass cockpits became more and  more ubiquitous. It is indeed a (slightly) derogatory term but I am not sure who started it.  Might be neat trivia to know.

I just did a google books search on various combinations of "steam gauge" and  airplane from 1930-1980 and got no hits, so I too suspect that the term wasn’t coined until the advent of glass cockpits.

@KorvinStarmast Probably not the first occurrance but in 1993 the Pilot Vehicle Interface document from the FAA mentions 'Older cockpits contained numerous "steam gauge" style indicators.'    http://bit.ly/2cXIbRq


text:
Where do airshow pilots practice?
I would assume that buzzing the tower and general hot dogging around the airport is prohibited, so how do airshow pilots get practice? Do they practice at high altitudes? If that is the case, how do they practice stunts that by nature require low altitude, like Bob Hoover's waltzing landing?

Check this out: http://www.waypoints.co.nz/media/wysiwyg/pdfs/Display_Flying_and_Low_Level_Aerobatics_Manual_-_First_Edition.pdf

They do it like this in Cambridge. (Flash video.)

Aerobatic pilots typically use "aerobatic practice areas" when they practice.  Many of the Part 91 rules which would need to be broken in order to practice aerobatics are waived within these aerobatic practice areas (such as the 1,500 ft. "floor" for normal aerobatics in 91.303(e)).
The FAA has to approve them, and their guidance includes a good description:

4. AEROBATIC PRACTICE AREAS. Aerobatic competition pilots, airshow pilots, and others who wish to practice aerobatic maneuvers not
  necessary for normal flight and below an altitude of 1,500 feet above
  ground level (AGL) must use a waivered aerobatic practice area.  These
  areas are not to be considered airshow sites.  The aviation community
  uses these practice areas to establish and maintain proficiency as
  well as enhance competitive skills in all the recognized aerobatic
  maneuvers. They are established by the waiver applicant in conjunction
  with the local FSDO and may have dimensions of several miles in
  various directions or be as small as a contest box; i.e., a cubic box
  with a dimension of 3,300 feet on all sides. Inspectors should be
  receptive to the establishment of these areas, consistent with safety
  and the efficient use of the NAS.  It is imperative that the safety of
  all nonparticipating aircraft be considered when issuing a Certificate
  of Waiver or Authorization for an aerobatic practice area.

An aerobatic practice area may be established over an airport if coordinated with airport management, and can be used to practice landings like those that Bob Hoover does.
Besides the special rules in these areas, it is also a good way to warn other traffic that aerobatics could be taking place because they are listed in the A/FD and a NOTAM is issued whenever they are hot.

Are there any "permanent" APAs like there are MOAs, or are these set up on a temporary basis for preplanned practice flights?

A lot of the maneuvers can be learned and practiced at higher altitudes.
In the US, the airshow pilots usually request a waiver from the FAA (to waive certain rules) so they can practice at lower altitudes.  The waiver will specify the location, hours of operation, who can use the waiver, which specific rules are waived (usually aerobatics within 4 NM of an airway, and/or certain altitude restrictions).
In the US, a lot of airshow pilots get their start competing in IAC aerobatic contests.  This gives them the opportunity to learn the maneuvers and get some very experienced critiquing.  As they progress in the sport they attempt more difficult maneuvers at progressively lower (but still safe!) altitudes.

In addition to what's already been mentioned, there's usually at least one day and more often several days of practice sessions at the field where the show is to take place before the actual event.
That allows the crews to familiarise themselves with the actual local conditions as well as the visual cues ("hey, there's a tall red chimney right where I need to start my turn, handy").
And for "buzzing the tower", you can of course practice that with anything really. A nice tall free standing tree for example, a chimney of an abandoned factory, anything tall and slender in an area where you're allowed to practice.
Or lacking that mark a spot on the ground and in your mind extend that up.
And oh, you can practice low altitude things at high altitude the same way, create an imaginary plane at say 10.000 feet, calibrate your altimeter to show 0 at that altitude, and now just fly like you would normally. Safe too, if you get things wrong and would end up flying into the ground, you now still have 10.000 feet before you splatter yourself.

Good points except for the 10,000 foot thing. Aircraft performance that high would be completely different than down low and most altimeters can't be adjusted that far either. 1,000 maybe, but not 10,000.

@Lnafziger just an example :)

I'm just suggesting a more realistic example. :)

3,000 feet would be a more realistic example


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How does a PFD handle unphysically abrupt changes in the parameters it's displaying?
This question is about human factors requirements in the design of software components displaying instruments in a primary flight display. (It's not about how to implement the software.)
Let's take an airspeed indicator (ASI) as an example. In a "steam gauge" ASI, the needles add some inertia to the instrument, limiting the maximum rate of change it can display. This is OK, because the actual indicated airspeed (IAS) has a much smaller maximum rate of change in the real world.
In a "moving tape" ASI on a primary flight display (PFD), a software component receives updates of IAS and changes the display appropriately. The human readability of the instrument depends on the changes being gradual, so the numbers gradually "wind around" like a physical instrument: if the numbers abruptly jump, it's hard for the pilot to notice and understand what has happened.
In normal circumstances, an abrupt jump in IAS (or altitude, heading, or other important flight parameters) cannot occur, because there are physical limits on the rate of change. But the software component just receives a stream of values, and it's possible that an error elsewhere in the system could cause an abrupt jump.
Is there typically a requirement on this software component to smooth the instrument display or handle this possible situation? I can imagine some possible ways of dealing it:

The display component has a limit set on rate of change (guided by the physical limitations and the HF limit on how fast a change can be displayed understandably), and it has to reject out-of-range changes (presumably tied to an EFIS/ECAM message). When the changes are in range, the display is updated immediately without interpolation.
The display component has to interpolate between received values by animating, so that even abrupt changes appear to "wind" the instrument. This preserves the readability of the instrument but will introduce some latency in the displayed values.
The display component has no special requirement, and protections elsewhere in the system ensure that it never has to deal with unphysically abrupt changes.

I understand that per-component requirements are unlikely to be published by any vendor, so I'm happy to take an unsourced answer if it's backed by personal experience. Even information from an experienced glass-cockpit pilot who has seen this error state first-hand would be appreciated.

I believe somewhere in the system there’s a low-pass filter of sorts before the display... not sure where though (that’s probably type specific, anyway).

Are you asking about a case where the airspeed data (for example) changes too quickly to be physically possible? If so, why would you expect the PFD to do anything other than report a failure? The G1000 will fail an 'instrument' display if the data is "invalid" according to the manual, but Garmin doesn't say exactly what that means, at least not in the manual. I guess it's similar for other systems.

In my experience, some level of filtering occurs, say from an incoming ARINC 429 data stream or from a sensor input. Most tape displays I have seen are of a rolling type, in that it doesn't just jump to the new value, but rather "rolls" there from the current value. The point is to emulate the behavior of an analog display if possible.

I did find this in SAE 6296 - 4.1.1.7 Smoothing
The indication of airspeed shall be smooth and free from irregular motion (jitter, jerkiness, or ratcheting effects) as the differential pressure or its electrical equivalent is increased and decreased smoothly.

@selectstriker2 That's very interesting, but it's specifically about not adding jerkiness when the input is smooth.

An abrupt jump in IAS can easily occur.  It's called "windshear".

Generally, PFD will smoothen the indication for most of the indicated data.
I don't know any 'legal' requirements for it, but as you mention, basic ergonomics require it.
I have first hand experience with Garmin G1000, so I'll try to explain its PFD behaviour as an example. (It's a bit hard to capture and post a video).
Most (if not all) 'graphical' indications are filtered with the rate (characteristic frequency) consistent with the expected rate of change of the relevant parameter: pitch/roll quickly (but still noticeably, about 0.3 s), airspeed moderately, engine temperature slowly (3-5 s). Digital only indications (say, battery voltage) are also filtered, and in addition their precision is limited such that the updates didn't happen too frequently (e.g. round 0.5 V).
The filter seems to be a second-order low-pass in most cases. For some parameters, notably the indicated airspeed, it is underdamped, which means the indication overshoots slightly for abrupt changes, and generally tends to oscillate to and fro for normal changes. This provides faster response while still being smooth.
An abrupt, unrealistic change of parameters per se doesn't cause a fault for PFD. It's just filtered as usual. However, significantly out-of-range values will fail the indication, but only temporarily, until sensible values resume. Generally, it's the job of the peripheral computers (ADC, AHRS, etc.), as well as of the integration unit (GIA), to detect faults and convey them in special messages. PFD is, after all, just a display.


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How does the GE H75 eliminate the need for hot section inspections?
Operators of the Pratt & Whitney Canada PT6 will be familiar with the need for hot section inspections half way to TBO. General Electric is touting the lack of hot section inspection requirements for their GE H75 engine. How did GE eliminate the need for the added inspections?

It looks like they use single piece rotors where the PT-6 uses blades connected to a central hub to form the rotor. They also use more forgiving metals like titanium.

this is because the fact that GE H series engines do not have fuel nozzles and feed fuel into combustion chamber through a rotating shaft. this design is much less sensitive to the fuel quality and combustion deposits in comparison with usual fuel nozzles


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How do airplanes regulate the output frequency of AC generators?
AC electrical buses are common in airplanes from light piston twins all the way up to the largest airliners. I usually see both a 115v and 36v AC bus with a 400 Hz output frequency. How do most airplanes regulate the output frequency coming from the AC generator?

Sometimes they don't have AC generators, but use inverters to convert from DC to AC.

This is probably not a good conversation to start here in the comments, but don't generators and alternators product AC current?

Actually, there are AC and DC generators (it's a generic term), but an alternator is a specific kind of generator which produces AC electricity.

Doesn't necessarily have to be moved, but wouldn't this make more sense at EE.SE, since this is essentially asking "How do you regulate the output frequency of AC generators?" I'm pretty sure it's done the same way in aircraft as it is anywhere there's an AC generator that needs to output a fairly stable frequency (i.e. every one of them).

@FreeMan So far as I understand normally that's done via a governer on the prime mover.

It's done using mechanical device called constant speed drive. Works almost the same as CVT transmission in a cars. The more complex thing is phase adjustment as airplane usually has multiple engines and generators. But that is not done as different generators always power different buses!

And in the A380 the mechanical drive is eliminated entirely I think.


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What are the rules of thumb for intercepting and tracking VOR and LOC courses?
Pilots training to become instrument rated must learn to intercept and track VOR and LOC courses. What are the basic rules of thumb all pilots should learn regarding picking a course for intercept and making corrections to maintain the course? How do they vary between VOR and LOC courses?

Voting to close as too board. Describing how to intercept a VOR course can easily take a whole chapter in an aviation textbook. What do you want to know? Scanning instruments? Crosswind correction? Back course tracking? Entry procedures?

I didn't ask for a textbook description. I asked for a rule of thumb. A rule of thumb might be something like "two bars of deflection is 4 degrees so divide in half and turn 2 degrees away from the deviation." I don't think asking for this is too broad.

I understand what you want to ask. My point is simply being, tracking VOR courses has so many subtopics; they are all "basic" rules and all pilots must learn them. The super simple rule is, if the needle goes right, turn right; if it goes left, turn left.

Does that help?

@mins Actually, yes this is super helpful. Thank you!

the rule of thumb for IFR flying, including intercepting VOR and LOC courses, is the 5Ts:

Throttle: turn the throttle to initiate a climb or descent
Turn: to the new inbound or outbound heading
Time: reset the timer to time the
new leg
Twist: the OBS to the new course you're intercepting
Talk:
if you are at a reporting point, you should now use the radio

I usually go with "Turn Time Twist Throttle Talk". Chanted it on every flight during my Instrument Rating. :D

The 5 Ts in my answer follow the aviate, navigate, communicate dictum

To track to a station track a radial with a To indication
To track from a station track a radial with a from indication
To track outbound turn your vor obs to a radial with a from indication and intercept where the needle is (left or right) within 90* (otherwise you will start tracking towards the station)
To track inbound turn your vor obs to the reciprocal heading and intercept within the 90deg* of the direction the needle is.  ( the reciprocal in crucial)

Basic vor intercepts will call for 90 * intercept to avoid crossing the station however this is amateur but ensures the task cannot be failed
They will call for 45* intercept outbound since you have no worry of cross the station.
Proficient pilots will intercept as required when tracking vor becomes second nature.
The radial your a/c is on can be found always by centering the needle with a from indication.  This will give the radial from the station that your aircraft is on.
Remember aircraft heading is not relevant , just the position of the aircraft I  relation to the vor
Vor reception 1.23 x sqrt ALT
 Vor is line of sight so the greater the ALT, the greater the reception distance.
I may have worded the first 4 rules wrong but they are fundamental!


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Are there ILS approaches where a non-precision procedure isn't allowed?
Are there ILS approaches where the LOC/non-precision procedure isn't authorized?

Yes, there are.
Note: This is as opposed to those ILS approaches listed as ILS or LOC in the title—such as KGEG ILS or LOC RWY 3—which do have an authorized LOC approach.
Special Authorization Cat I ILS, and Cat II & III ILS approaches do not have authorized LOC procedures. These are precision only approaches.
See KGEG approaches, for example. Specifically, the ILS RWY 3 (SA CAT I), and the ILS RWY 3 (CAT II & III) approaches do not have authorized LOC procedures.
See also this screen cap of the KGEG ILS RWY 21 (SA CAT I) approach:
[][6]

the SA approach gets 50 foot lower DH than the ILS/LOC 3. Its not clear that the ILS/LOC 3 is a completely different approach, even though it has a different plate. The LOC 3 minima are typical for a LOC approach

@rbp I'm not sure what you are trying to say. Do you consider Cat II & III approaches to be the same approach as their higher DA Cat I counterparts? If a distinct plate is not the denotation of a distinct approach, what is?

I'm trying to point out that there's something going on here that's unclear. The CAT I SA approach is clearly a derivative of the ILS approach, as is the  CAT II & CAT III. But why isn't the CAT I approach melded into the CAT II & CAT III plate, with another "CATEGORY" entry? And why are the CAT II and the CAT III approaches not separated into two separate plates, since they share differ in the same way as CAT I SA and CAT II?

@rbp I don't know. Seems pretty standard to me. See these three KMSP ILS 12L approaches: CAT I, SA CAT I, and CAT II & III. I suppose you could ask a new question about that, if you'd like.

Your links are broken.

@sean Links to specific approaches have been removed. I do not know of a way to link directly to these as the URLs are updated every 28 days.

Van Nuys has two, ILS Y RWY 16R and ILS Z RWY 26R. Both use the localizer on  111.3 but have different stepdown fixes and different missed approaches. Radar is required for the missed on Z.


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What common forms of deice and anti-ice exist and what future alternatives are being researched?
For the leading edges of aircraft's flight surfaces, there are a few more common deice and anti-ice methods available. What are the most common systems? What are the alternatives? Is there any research going into alternatives where new technology might provide better or more cost effective solutions?

See: How do large airliners de-ice in flight and AOPA Aircraft Deicing and
Anti-icing Equipment. Does it fully answer your question?

I'm familiar with that questions and I have that AOPA flyer in my CFI notebook. These questions cover the first part of my question, but I also wanted to put together a question that would result in an answer that also covered emerging technologies. The Wikipedia page for ice protection actually provides a good overview of existing, less-common and emerging technologies. I may use that as a basis for writing my own answer to the question.

Okay. Just in case this is not already in your search results, a couple of ideas: How to De-Ice a Drone using Carbon Nanotubes, also  Poison dart frog inspires new way to de-ice planes and older Zdobyslaw Goraj's article on the topic

@mins Thanks for those references!

In general, deicing (removal of ice after it had formed) and anti icing (prevention of ice formation) methods used are:

Image from GKN Technology: Leading the way toward more efficient aircraft

Mechanical which simply pushes the ice off the leading edges. An example is the pneumatic deicing boots, which is the oldest method used where an inflatable rubber boot is used for removing accumulated ice from the leading edges.

Source: quora.com
"Deicer (PSF)" by Pearson Scott Foresman - Archives of Pearson Scott Foresman, donated to the Wikimedia Foundation→This file has been extracted from another file: PSF D-240001.png.. Licensed under Public Domain via Commons.

Heating In large aircraft, the wing (and tail) leading edges are heated by engine bleed air (electro-thermal heaters in case of Boeing 787) for anti-icing and de-icing.

Image from Aircraft Anti-Icing Systems by Leslie Mehl and Annie Parsons

Chemical de-icing systems use dry or liquid chemicals designed to lower the freezing point of water (various salts or brines, alcohols, glycols); or by a combination of these different techniques.
Fluid de-icing systems which use de-icing fluid from a storage tank and fed through micro-filters to a number of porous metal distributor panels. As the fluid escapes, it breaks the adhesion between the ice and the wing and the airflow carries it away, creating the so called 'weeping wing'

There are a number of other de- and anti- icing methods are also available/under development, such as:

Electro-impulse method used high-voltage capacitors, which are rapidly
discharged through the coils installed just inside the skin of the aircraft leading edge, resulting in a electromagnetic repulsive force (on the aircraft skin), throwing ice in all directions. However, the electromagnetic interference and structural fatigue associated with this method limits its application.
Electro- Expulsive Separation System An electric current runs through parallel layers of flat, copper ribbon. When a large pulse of current is passed, a repelling magnetic field is created, causing the upper conductor to jump less than a twenty-thousandth of an inch. The resulting high acceleration causes the the ice to break into tiny particles that fall from the airplane's surface.

Electro-Expulsive Separation System shatters and ejects ice from a wing model in a wind tunnel test from ipp.nasa.gov

Electro-Mechanical Expulsion Deicing System, whose principle of operation is given by the developer as,

A microsecond duration high current electrical pulse delivered to the actuators in timed sequences generates opposing electro-magnetic fields that cause the actuators to change shape rapidly. This change of the actuator shape is transmitted to the erosion shield of the LEA causing it to flex and vibrate at a very high frequency. This rapid motion results in acceleration-based debonding of accumulated ice on the erosion shield.

Image from An Overview of the Deicing and Antiicing Technologies with prospects for the Future by Zdobyslaw Goraj

Ultrasound Some research is also going on into vibrating the wings using ultrasound to remove ice formed.
Shape memory Alloys have also been proposed to be utilized for deicing and anti icing, with their shape changing properties being used for ice removal when required.

Image from An Overview of the Deicing and Antiicing Technologies with prospects for the Future by Zdobyslaw Goraj
There has also been some research into usage of carbon nanotubes for this purpose.

Do any of these systems address the problem postulated in American Eagle flight 4184 where supercooled water can freeze past the icing boots?

@TomMcW -- runback (or aft of leading edge) ice has not been seen as a concern with thermal anti-ice/deice systems so far; weeping wings are presumably protected by deice fluid running back along the wing upper surface.

This depends on the plane but generally speaking there are,
De-Ice Boots which work by allowing ice to build up and then they are inflated, thus cracking the ice off the leading edge.

(source)
Heated Leading Edge Relatively self explanatory but it simply heats the leading edge either electrically or via hot engine bleed air.

(source)
Weeping Wing (Chemical) is a technique used on some small planes where de-ice fluid is pumped through small holes in the wing leading edge to prevent the ice from building up. This presents 2 separate problems that the other systems don't suffer from. Aside from the weight toll you take for the system its self de-ice fluid is heavy and imparts another useful load toll. You also run the risk of using up all your fluid while in flight.

(source)
The FAA has a nice briefing on it you can find here which outlines all the various types of systems and the risks that come from icing. Their official list of icing prevention is

Heating surfaces with hot air
Heating by electrical elements
Breaking up ice formations, usually by inflatable boots
Chemical application

There are four common forms, and not all are available to all aircraft:

Heating the leading edge of all surfaces. This is done either by bleed air or electrically, and both will reduce engine thrust. Due to the high energy demand, electrical heating is mostly used on air intakes or propeller roots.
Inflatable rubber boots. They are more economical, but must be operated correctly. If activated too early, the thin ice will not break off, if activated too late, the thick ice will prevent them from inflating.
De-icing fluid: This requires fine holes in the leading edge through which a de-icing fluid is squeezed to break the bond between ice and structure. Some Beech Starships used titanium leading edges with laser-cut holes. Earlier systems, like that on the BAe-125, used sintered metal sheets which had tiny pores.
Fly faster: Military jets don't need anti-ice, they use the stagnation heat generated by a higher flight Mach number. Generally, flying Mach 0.9 or above is enough to avoid trouble in light icing conditions.

Concerning future means: It is difficult to make predictions, especially about the future.


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How reliable are Lycoming and Continental general aviation piston engines?
Statistically speaking, how reliable are Lycoming and Continental general aviation piston engines? What I'd really like to either find or build is a table showing the probability of experiencing engine failure on a properly-maintained piston engine for most of the common models of engine. Is the data out there?

reliable enough to get certified as aircraft engines which is no mean feat.

Short (pilot's) Answer
"Reliable enough for you to fly behind one, flaky enough that you should always expect them to fail at the least convenient moment."
Short (Mechanic's) Answer
"More reliable than the pilot!"

Longer Answer
You can't really know the failure rate, but you can know the accident rate attributable to engine failures.
The NTSB looked at this back in 1972 and Embry-Riddle still has the report available. It's very interesting reading, and goes into great detail on the specific causes of engine failure.
Totaling up everything they classified as "engine failure" gave a failure-related-accident rate of just under 18 per 100,000 hours (i.e. "Assuming proper maintenance you could theoretically fly 5,000 hours in piston GA aircraft before you'd have an engine-failure-related accident.")
There may be a more current NTSB study on this, I honestly didn't look too hard as I expect the numbers to be broadly similar today.
The 24th Nall report shows 61 "powerplant" accidents (all engine types, and including the propeller and associated systems) - the number is not broken down per 100,000 hours but doing a little extrapolation from their other figures it works out to about 0.4 accidents per 100,000 flight hours (or "Assuming proper maintenance you could theoretically fly 200,000 hours in piston GA aircraft before you'd have an engine-failure-related accident.")
The mechanic's answer of "More reliable than the pilot!" comes into play when you look at the pilot-related accident numbers: In the 1972 NTSB report I cited engine failures made up 13% of the total accident figure. In the 24th Nall report all mechanical accidents were 14% of non-commercial fixed-wing accidents (17% of commercial accidents) - that includes a number of other systems (e.g. landing gear) which are unrelated to the engine.

Do you know if any of these "engine failure" statistics include fuel exhaustion/mismanagement? That seems to be a very common cause of engine stoppage, and it shouldn't reflect on the reliability of the engine.

The wording "fly 200 thousand flight hours before an event occurs" is false, because the "per flight hour" is just a probability, and the unwanted event can come any time. If someone could really tell that the failure would come at a special time, they would simply correct the problem just before that special moment. ;)

@FredLarson I know in the Nall report fuel exhaustion or fuel starvation/mismanagement are considered "Pilot-Related" rather than "mechanical" (it's not the engine's fault you weren't giving it any fuel - it wanted to run and you wouldn't let it!). The NTSB classifies it similarly, but in the 1972 report they appear to have included these figures as "engine failure" (with a more detailed breakdown later on in the report).

@GürkanÇetin Hence the word "theoretically" in those statements. Lots of things look good in theory - in practice "per-hour" statistics are very much like "per capita" statistics: They give you some useful information about the aggregate population (the GA fleet), but tell you nothing about a given individual (the specific engine you're flying behind today) :)

@voretaq7 Phrasing it as "on average you could fly 200,000 hours" might be more technically correct and illustrates the point.

That data may not be directly available but you may be able to piece it together. This article has some of the only numbers I have ever seen (although they may not be 100% accurate). Here are some random facts on engine failures that have no sources quoted so take it for what you will. There is some interesting info on why the engines fail here and here. Your best bet for piecing the information together is to look over the actual NTSB reports. For this you are going to want to pull them and have a way to comprehensively sort and filter them (which is really a computer science question not an aviation question). Since the plane is listed you should be able to extrapolate the engine from the report that way. You can also find some discussion on the matter here as well.
The issue with building a chart like this is there are many many variables and generally speaking (at least from the NTSB reports I have read) engine failures are often linked to improper maintenance or improper use more than they are related to an engine component simply breaking. In many cases it only takes one failure for an AD to be issued and the problem to be solved. Engines like the more common Lycomings and Continentals you find in GA planes today have been around for some time and proven to be reliable and simple. Mechanics know them through and through and there are years of validation to support TBO numbers and things like that.
This thread seems to provide real numbers pulled from NTSB reports (at least thats what the guy claims). Its an interesting read if the numbers are correct. The fact remains that engine failures are rare (in the grand scheme of things) but do occur and should always be prepared for.


text:
Where is the only Aerostar 800 ever built?
The Ted Smith Aerostar has a very interesting history. Wikipedia has a list of all the models that were built. There's a note there about an Aerostar 800, only one of which was ever built. Does anyone know where that 800 is today?

According to this page the airframe was donated to Embry-Riddle Aeronautical University:

The Superstar airframe was later used as the prototype Aerostar 800. The prototype 800 was the Superstar airframe with two more seats (due to a 32” extension of the cabin) and featured two 400-hp. Lycoming engines. The 800 was under development when Ted unexpectedly passed on in 1976. Piper continued development of the airplane as a replacement for their P Navajo but never certified it and eventually donated the airframe to Emery Riddle [sic] Aeronautical University.

This is the only reference I can find to the ultimate location of the Aerostar 800.

@Pondlife, you just beat me to that edit :-)

Even though I was searching around their site I never once picked up the misnaming in the linked article. Thanks

@DeltaLima :-) Amusingly, someone has even created a Facebook page for "Emery Riddle Aeronautical University" in Kentucky, which is a real ERAU campus. Hopefully the person isn't a student, or that would be really embarrassing...

@Pondlife This Page is automatically generated based on what Facebook users are interested in.... Facebook users are obviously interested in mistyped university campuses :)


text:
Does burning fuel to get to your max landing weight violate any regulations?
Consider a hypothetical situation where where an unexpected tailwind will cause a flight to arrive at its destination above maximum landing weight. After reviewing all reasonable changes to altitude and airspeed, it is clear that on the flight plan route nothing short of a hold or delay vector would allow for a landing within the weight limits.
The SIC suggests including the dispatcher in the decision, and asking for a delay vector or or hold that adds 8 minutes to the flight.
The PIC elects to land overweight, citing a regulation in FAR 121 that precludes any undue delay to burn fuel. Not a specific regulation, just that there is something like this in there.
Is there a regulation in FAR 121 (or any of the other 14 CFR/FAA regulations that govern the flight) that would be violated by adding distance to the route or a hold in order to facilitate additional fuel burn and a landing within the limitations?

There is a bit of a logical gap in this scenario.  The only situation where you'd have enough fuel load to be at MTOW at departure and need to fly a significant time to get below MLW, would be a trip that is long enough that you simply couldn't arrive above MLW in any normal tailwind.  For a trip where a tailwind could get you to destination with very little fuel burn where you could arrive above MLW, you wouldn't have started with that much fuel in the first place.  Maybe if the airline was tankering fuel for some reason but that would be about it.

I can't see this scenario being possible. MTOW and MLW aren't generally far apart, you don't have to fly for long.

@GdD  A Boeing 747-8 has a MTOW of 987,000 lbs and MLW of about 675,000 lbs.  That's over 300,000 lbs of fuel and about 2/3 of the max fuel capacity.

This scenario isn't common but it isn't exactly rare, either. You take off with a full plane & lots of fuel for holding & an alternate, planning to arrive just at max landing weight. Then, due to shortcuts and/or better than forecast tailwinds, you under-burn & see that you'll arrive above max landing weight.
First, the hypothesized rule in Part 121 doesn't exist. Absent the Captain's use of his emergency authority (which does NOT require declaring an emergency to invoke, but which DOES have to be reported after the fact), what you can't do is "just go ahead and land overweight." That would be deliberately violating an operating limitation on the aircraft, and that's bad.
Second, there's typically no need to involve the dispatcher... just burn the gas. Holding, or extended vectors, or an early descent, or extending the gear way early... take your pick of what works best in your situation & then make it happen. Not a big deal.
Burning extra gas (really, just burning all the gas you'd planned to burn with the flight plan) is NOT a violation of anything in Part 121. On the contrary, intentionally landing overweight - in the absence of a circumstance making that the safest option - would be a violation.
Listen to ATC long enough, and you'll occasionally hear somebody ask for a delay to burn the extra gas. ATC can easily accommodate that; I've never heard it treated as if the crew is asking for something strange or suspect. Sometimes winds or shortcuts put you in that situation; it's nobody's fault, and it isn't a problem to burn the planned fuel.

Could one simply burn up the fuel without delaying, by intentionally avoiding the most efficient flight envelopes? Fly at 16000 when able to fly at 35000, fly at max speed instead of best cruise, etc.

@Harper, yes, those are ways to burn fuel faster. Each has its pro's, con's, and limitations. For example, cruise altitude may need to be high enough to overfly bad weather, so that may be a bad choice "today". Depending on the flight duration, a higher cruise speed may not burn enough more gas to solve the situation. But both options could certainly be considered.

I did a little rooting around and from what I can find and from my own general sense the answer is no.  No regulation could possibly be issued based on what is effectively a somewhat abstract environmental goal (or maybe an objective of really really cheap airline) that supersedes regulations related to safety or efficiency in the system.
That being said, maybe, theoretically, an airline may have done a business case where in that situation they decided the costs associated with the need to do an overweight landing inspection (basically just maintenance manhours as long as they crew does a nice gentle landing) was less than the cost of "wasted" fuel, and the airline would therefore authorize capts to land overweight if the wasted fuel was more than some threshold, but I think that is kind of "out there" and is pretty unlikely. I've never heard of such a policy on the Regional side of things, and perhaps one of the mainline-knowledge guys here can pipe in.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Why do some pilots misuse (troll) the GUARD frequency?
When flying I almost always monitor GUARD, VHF 121.5 on my second communications radio. It's almost a daily occurrence that I hear someone transmit the words "work work work" or a long, theatrical "GUUARRDDD!" as a response to someone calling for a ramp taxi clearance on the wrong frequency.
It is interesting that these particular responses are so prevalent.
Has anyone studied this misuse of the guard frequency to determine if there might be a cultural source?
At least in my experience with the last decade of aviation, there hasn't until fairly recently but such common use of the guard frequency for communications which aren't pertinent to its purpose. Has the FAA taken any actions on pilots for misusing the guard frequency in the way mentioned in the first paragraph?

If you are going to vote to close, give me a comment and a chance to improve the question.

I don't know if there's any good, authoritative answer here unless the FAA or someone else has ever conducted a study. IMO, some of the calls on guard are a mild form of trolling, you might look into what motivates trolls in general. But I'm sure there are other ways to look at it too, e.g. you might charitably say that some pilots are trying to use 'humor' to remind/guide/correct others. In other words, I have no idea :-)

I've had "transmitting on guard" whilst conduction a practice pan!  Swiftly admonished by the D&D cell. (UK).

You can always edit your question, whether closed or open. At the moment, this seems to be about ready to be re-opened w/o any editing at all, though. The most important part would be knowing why it's being VtC'd (you should have enough rep to click the 'close' vote button to see what people are voting on to get a hint at it, at least.)

Every field has its bottom 2%, and some of ours regularly self-identify as such on 121.5.
Sigh.
The "work work work" refers to this video (start about 2:55 for the relevant section).

Was the downvote from someone who enjoys transmitting silly comments over the emergency frequency?  Other explanation?

Maybe the DV is because when that YT video disappears, it will become meaningless text. Maybe at least give some identifying info so the video could be found again in the future.


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Is a radio call required when vacating an altitude after being given a discretionary descent?
When operating a flight under these conditions:

In the USA
Under the FAA jurisdiction
Given a descent with pilot's discretion by controller
Operating on an IFR flight plan

Is a radio call required when vacating the altitude that was occupied when given the discretionary descent?

Great question! I just answered on the duplicate question, hope it gives you what you were looking for.


text:
What is "picture flying" and does the FAA define it?
What is "picture flying" and does the FAA define it in any of their literature?
Here is an example situation. You are instructed to depart using a SID. The SID states that at 1.5NM from ABC VORTAC a left turn should be made to heading 360. Your FMS allows you to draw a 1.5NM ring around the fix on your moving map, so you draw the line. When the little airplane is at the line, you make the turn. Anecdotally, I have been told this constitutes "picture flying" and isn't a legal way to comply with instructions from a SID or other procedure. The legal method would be to tune the VORTAC and make the turn when the DME reads 1.5NM.
One could make the argument that the DME is as inaccurate as the visual estimate from the picture flying. Aircraft climb at different rates and the angular distance affects the straight-line distance across the ground, especially if the instructions are something like, cross 20NM from ABC VORTAC at 10,000 feet.
Any definition or clarification from FAA publications or letters would be appreciated.

What's the difference between what you described, and using GPS instead of DME?

There is potentially a difference between "the point which is actually 1.5nm from ABC" and "the point at which the DME reads 1.5nm". I treat it analogously to your indicated altitude relative to a local altimeter setting, versus your exact actual height above sea level.

@ymb1 Yes, maybe. To me, ryan's describing an FMS that's capable of identifying a point 1.5 DME from a VORTAC, and I don't really see what the difference is between that and a GPS that does the same thing. Both instruments load the VORTAC's position from a database (I assume) and they both tell you when you're 1.5 DME away. So I don't really get what's different about his scenario, although perhaps that's exactly the question!

I can't prove a negative, but as CrossRoads pointed out, the phrase "picture flying" isn't used on faa.gov. At least, neither Google nor faa.gov's own search engine turn up any hits.
I searched a bit further and I did find one specific match in a Bendix advert in the Feb 2, 1953 edition of Life:

Picture flying is the name pilots give to flying with OMNI-MAG. Merely by watching the pointer the pilot always knows where he is,
  where he is going, and how to get there

There's no real technical detail in the advert (it's actually an advert for Bendix television sets!) apart from mentioning that the OMNI-MAG uses VHF radio, but based on the picture it looks like a VOR receiver.
So, given that the FAA seems not to use the phrase at all and the only exact hit I could find was from 1953, I suspect that "picture flying" is an obsolete phrase for following a visual course indication. Before VORs, pilots used audio signals from a four-course radio range and the advert even mentions that they won't have to listen constantly any more.
That makes me think that the phrase arose around the time that radio navigation moved from audio to visual signals, to indicate that the pilot could now look at a visual indicator rather than just listen. That transition happened in the 1950s, so it would fit with the advert's publication.

+1 for revealing that Bendix made televisions


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Does it violate any regulations for a bag to sit on the flight deck floor?
Pilots who fly the Canadair Bombardier Regional Jet or CRJ aircraft know first-hand how cramped the space on the flight deck is. It's really a business jet cockpit, not the flight deck you'd expect on a transport category aircraft. I have heard that it's not uncommon for pilots to keep a small lunchbox on the floor of the seat next to them.
Some pilots say that a bag cannot be stored there next to the seat and that if an FAA inspector were to see the bag, there could be consequences.
Is there a regulation that storing a bag in this way violates?

"On the floor of the seat next to them"... you mean on the floor behind the seat don't you?  Or on the center isle floor behind the console?   I've put stuff on the floor behind the seat.

I’ll post a pic to clarify.

There are some relevant links in the Cabin Saftey Index document under "crew baggage" indicating that all bags must be restrained. The document points to

§121.576   Retention of items of mass in passenger and crew
  compartments.
The certificate holder must provide and use means to
  prevent each item of galley equipment and each serving cart, when not
  in use, and each item of crew baggage, which is carried in a passenger
  or crew compartment from becoming a hazard by shifting under the
  appropriate load factors corresponding to the emergency landing
  conditions under which the airplane was type certificated.

The question remains if the cockpit is in anyway different than a "crew compartment" but I would say that could be applied to your question.
However if the bag in question is a flight kit then different rules apply which can be found here:

A. Flightcrew Flight-Kits. Particular attention should be given to
  compliance with part 121 regarding restraints for any baggage carried
  on the flight deck. Flightcrew flight-kits are not items of crew
  baggage. This policy also applies to aviation safety inspectors (ASI)
  and additional flightcrew members. While it is logical that
  flight-kits be placed so that movement is restricted, the FAA does not
  intend that they be restrained in a manner that would interfere with
  the needs and functions of the flightcrew.

I can not find a further definition of "flight-kit" and/or if you can or cant put your lunch in it.


text:
Has Jeppesen announced plans to stop supporting the Microsoft platform for Flight Deck Pro?
I heard a rumor around the water cooler recently that Jeppesen plans to drop support for Microsoft and have continued development of Flight Deck Pro EFB software only available on Apple. Has anyone seen anything that could confirm or refute this?


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Why are turbine blades not made out of titanium, only compressor blades?
According to this video on jet engine blades, titanium is never used for the turbine, because it "melts and burns at the temperature of the flame". Only the blades of the compressor are made of this material.
However, the melting temperature of titanium is higher than that of any steel alloys I could find, and titanium produces a protective layer of oxides on the surface. What other properties of titanium make using it impossible?

tungsten has a melting point 1.5 kK higher than titanium

But tungsten has a much higher density than steel, unlike titanium.

but tungsten based alloys also have a high melting point

Wikipedia claims "[m]odern turbine blades often use nickel-based superalloys that incorporate chromium, cobalt, and rhenium." I have no idea what a superalloy is, though.

@raptortech97 http://en.wikipedia.org/wiki/Superalloy :)

@ratchetfreak Titanium versus tungsten is more complex than that. Typically, the "titanium" used is actually a titanium-carbon alloy, just like steel is an iron-carbon alloy. I guess you could call it Titanium-steel. The exact percentages of Ti/C and W/C will determine their properties. Don't forget there is also Tantalum (Ta) to deal with!

Swarf from Titanium (random eBay offcut alloy) lights off like magnesium ribbon right after work-hardening and blunting an HSS drill bit. Gave me a bit of a surprise... But it suggests there are drawbacks to operating Ti components in high temperature environments.

Titanium is unsuitable because it will react with oxygen and carbon at high temperature, well below its melting point, making it very hard and brittle. Welding titanium is very complicated because it needs to be shielded extremely well from any oxygen when hot. Ti$_3$O will form above 500°C, and Ti$_2$O above 600°C.
Initially turbine blades were made of steel alloys, but they have been displaced by nickel alloys.
Also, they operate in an environment which requires constant cooling, so they can be 200 - 300°C cooler than the turbine entry temperature of the gas coming from the combustor(s). Modern turbine blades are hollow and have a perforation at their leading edge. Pressurized, relatively cool air is forced through the blades and the perforation and flows around the blade's surface, creating a cool sheet of air to shield the blade from the hot gas. Also, before entering the turbine the gas is accelerated, which already lowers its temperature. See the plot below of parameters inside an older engine taken from this source.

Shortly past the fuel injectors the maximum gas temperature of approx. 1800°C is reached, which drops to 1100°C at the entry to the first turbine stage. Note that this temperature has been raised to 1500°C in modern military engines! At the same time, the highest temperature is connected with the lowest speed (30 m/s), and the flow accelerates to 200 m/s directly before entering the first turbine stage.
Titanium in contact with oxygen would lose a lot of its strength at these temperatures, even though its melting point is at 1650°C.

In addition to cooling and nickel alloys, two other technologies are used: monocrystalline casting and thermal barrier coatings.
Thermal barrier coatings, in concert with cooling, allow operation at close to the melting point of the base material (as referenced above). TBCs usually consist of yttria-stabilized zirconia, which has very low thermal conductivity and a coefficient of thermal expansion close to that of nickel alloys. This makes it incompatible with titanium, which has a lower CTE; The different growth rates induce stress into the coating, eventually cracking it.
In addition, YSZ is oxygen-permeable at high temperatures. This can be reduced (temporarily) by an underlayer, but eventually oxygen penetrates to the substrate. Nickel alloys are substantially more oxidation resistant at temperature than titanium, as previously mentioned, so they also are more compatible with TBCs in this way.
The other technology used in hot section rotating components is  monocrystalline casting. Simply put, larger crystals resist creep because they are less likely to combine with other crystals, and you don't get larger than a single crystal. To my knowledge, there is nothing about titanium casting alloys that makes them incompatible with single crystal casting.


text:
Are there security checks on private flights in your own plane?
On commercial flights there are some "typical" security checks - metal detectors, luggage X-rays, etc. - are there similar security checks if you're flying in your own private plane?
Are there different or additional security checks when flying into other countries (such as a trip from Canada to the United States)?

I've adjusted the wording and (re)closed this as a duplicate of "How does security & baggage checking work in regards to a private jet?" - If that doesn't address your question please edit it a bit more to make the distinction clear and I'll reopen it.

There are special security considerations flying into DCA (among other things, background checks for crew members, a passenger manifest approved by TSA, screening by TSA at the last stop before DCA, and a TSA-approved armed security officer on board). Not sure if anywhere else is like that (I'd assume they'd mostly just say "no GA" if they were going to put similar rules).

No, at least not at the Class C and D airports I have been to. There is just a locked gate with an attendant who makes sure you are either flight crew or are boarding a flight. This is to prevent the possibility of a random person walking around on the ramp.
The PIC of the aircraft, of course, may question you ("your hunting rifle is unloaded, right?") or may search your bags or body cavities or whatever he wants to do before he will let you get on. It depends on the situation. For a charter flight normally they will just verbally talk to you to make sure you aren't unknowingly bringing anything dangerous aboard.
When you fly into a country from a different country, everybody has to go through customs. So, what happens is that you all wait around in the lobby of the GA terminal while some dude from the airport examines your customs forms and goes through your luggage. Sometimes they will search the whole plane too if they want to be dicks. In smaller airports, like in a Caribbean island, you will be routed through the same customs lines that commercial passengers use.

The question asks about "your own plane," implying the asker is probably PIC, so the references to the PIC doing searches seem extraneous.

@raptortech97 Good point.

You also need to remember that for a small plane, the "airport" might be a dirt/grass strip in the Idaho mountains, or a stretch of dry lake bed...

@jamesqf +1 for recognizing that Idaho is a state. You'd be amazed...

@raptortech97 On every flight that I do (for work), I am the PIC and am flying the owner of the plane.  Just because you own one, doesn't mean that you can fly it or be the PIC.  ;-)

Depends on the pilot. If I know one of my passengers well, I'm not security checking them, other than a reminder about dangerous goods.
If I don't know one of my passengers, then I'm doing a verbal confirmation that they don't have anything on board that I don't want on board, and if they're at all shifty, I'm checking more thoroughly.
I don't own an x-ray machine.

Hows the process of departing from a larger airport? I dont have a license just wondering about this. Is it similar to having youre own car?

At larger airports, general aviation aircraft generally use their own, smaller terminal, which let people basically walk through to the airplane with the pilot.

I worked at a general aviation airport in Canada for 10 years. Security consisted of 3 strands of barbed wire and a padlock on the gate. Security checks before boarding anyone consisted of whatever you wanted to do, including nothing.
Flying to the States simply required that the first landing be at any airport with Customs and Immigration.


text:
Why pilots would leave the cockpit in a short flight?
I've occasionally read about pilots being locked out of the cockpit in flight, and was wondering:
Why might a pilot leave the cockpit during a short flight (1-2 hours)?

And when you read about pilots being locked out of the cockpit, the article didn't mention why they'd left?

Just from a human standpoint:  You have to pee, when you have to pee. While the bladder reached a regular "time interval", "much liquied" (everybody should drink on a plane due dry air or you become easily sick), "being nervous" or because your bladder doesn't work normally (ill). Furthermore like all humans a crew needs to stand up and move their feet (again, it healthy and keeps awake) and chat a little bit with the crew. As passanger I would appreciate to see that the pilots have a little bit contact to the rest of humanity on the plane :)

The cockpit of some airliners lacks a lavatory.

Cockpit layout from AviationKnowledge.wikidot

This is discussed in Skybrary: Flight Deck Security

Locked Door Flight Safety Issues
  ...
  Physiological Need. Naturally, the need for flight crew to use toilets, access designated crew rest facilities or be supplied with food and drink, requires access through the flight deck door during flight. Procedures for door opening mean that egress and access will take longer with the result that the flight deck crew are not always able to go to the toilet at a time of their exact choice, which may cause them to be distracted and, exceptionally, might exacerbate an existing underlying medical issue in a way that would not otherwise have occurred.
  ...
  Longer term, design change could also ensure that all operating flight crew should be secured on the flight-deck before the passenger boarding doors are closed prior to departure and remain secured on the flight-deck until after the passenger doors are opened at the destination. This would prevent any unlawful entry from the cabin and minimise any unlawful seizure by a single flight crew member.
  To enable this, existing aircraft could be modified and new aircraft designed with all required crew facilities forward of the secure flight-deck door. On short/medium haul aircraft this would require a toilet, safe food & water storage and a reclining crew rest seat. Additionally on aircraft used for long range operations where in-flight relief is required provision of bunk/s.
  This is not a new concept, many long range aircraft already have toilet and crew rest facilities forward of the secure flight-deck door.

Do you have to pee in a 90 min. flight?

@JuanMateo no, but you probably have to pee sometime during the day, and with the short turnaround times, I'm pretty sure there's no chance to do so on the ground

When you've gotta go you've gotta go, and I'd much rather have a pilot who can fully concentrate on landing the plane than one who's trying to hold it in.

90 min is a wrong assumption. First, the flight was 2h20' long, second there are pre-flight and post-flight duties, that would make it longer.

Is there an actual image of a toilet inside the cockpit. Also can't the pilot's use Travel John?

@JuanMateo middle of a flight would probably be the best time to take a pee, since on the ground in pre-flight and post-flight duties the pilots are busy, but while the plane is cruising on a straight path then there's practically nothing to do and a single pilot can easily handle it - I mean, it's the appropriate time for pilots to take a nap in longer trips.

@Firee Notice that the door to the toilet in that image opens to outside the flight deck (i.e. to the passenger cabin.) Most airliners don't have dedicated lavs for the pilots. That would be a really big waste of space and weight.

@reirab : Why can't they provide a door to the lavatory from the inside, so that the pilots don't have to leave the confines of the cockpit..

@Firee They could, but that would then make the lav a second potential point of access to the flight deck, which is probably more dangerous, as someone could attempt to break in without being noticed until they've already gained access to the flight deck. Additionally, there's not much extra space for another door either in the lav or on the flight deck in most aircraft. For example, in the diagram above, the sink is on the one side of the wall between the lav and the cockpit and the circuit breakers are on the others side, so both would have to move (and there's no extra room for the sink.)

@Firee Granted, in the particular configuration shown in the image above, access to the flight deck probably isn't as critical, since it's presumably a military aircraft (civilian transports typically don't have a station for an air-to-air refueling operator.)

Why having toilets in theaters for a 90 min movie? Or in tube? Why should pilots be forbidden to have prostate problems like the rest of the people? Wait until you're 55 and you'll likely understand.

@reirab: Maybe some kind of solution similar to fighter aircraft pilots, could be looked at

@Firee I'm thinking the pilots would not like that. Especially not the female pilots. Why bother when there's a perfectly good lav a few feet away? Incidents like the Germanwings flight can be solved by having an FA take the place of a pilot when he leaves the flight deck. This has been standard procedure for a lot of U.S. airlines for a long time and has, in the wake of the Germanwings incident, also become recommended practice in Europe.

The FAA provides the following reasons for which a pilot is allowed to leave their assigned duty station (i.e. their seat in the flight deck) in 14 CFR §121.543 Flight crewmembers at controls:

(b) A required flight crewmember may leave the assigned duty station—
(1) If the crewmember's absence is necessary for the performance of duties in connection with the operation of the aircraft;
(2) If the crewmember's absence is in connection with physiological needs; or
(3) If the crewmember is taking a rest period, and relief is provided—

Case #3 generally applies only to long-haul flights where one or two relief pilots will alternate duty with the initial pilots, allowing each of them to have a rest period.
Europe's EASA has similar regulations. See CAT.OP.MPA.210 in this document (on pages 101-102).

CAT.OP.MPA.210 Crew members at stations
(a) Flight crew members
(1) During take-off and landing each flight crew member required to be on duty in the flight crew compartment shall be at the assigned station.
(2) During all other phases of flight each flight crew member required to be on duty in the flight crew compartment shall remain at the assigned station, unless absence is necessary for the performance of duties in connection with the operation or for physiological needs, provided at least one suitably qualified pilot remains at the controls of the aircraft at all times.

So, in summary, a pilot can leave the flight deck on short flights if:
1) The pilot needs to go to the bathroom.
2) The pilot needs to perform some action relevant to flying the plane (such as going to the back to physically inspect some part of the plane, like in QF32 or United 811.)
Related question whose answers also mentions these regs: Are two people required in the cockpit at all times on large commercial aircraft?

Might want to at least link to the question where this is info is also used.

@fooot Honestly, I was trying to decide whether to vote dupe close on this one. However, those answer really answer this question, but not the one they're posted on, so I wasn't really sure how to address that. Nevertheless, I'll add a link.

Well those regulations don't totally answer whether a second crew member is required at all times (just that it's not in the general operating rules), but they don't provide all the exact reasons a pilot may leave the cockpit either. Thanks for adding the link.